Fluid heat exchange installation and method of forming the same



J. P. CRAVEN FLUID HEAT EXCHANGE INSTALLATION AND METHOD OF FORMING THESAME Filed Oct. 1945 Jan. '2, 1951 I INVENTOR :Jofm P Craven ATTORNEYPatented Jan. 2, 1951 FLUID HEAT EXCHANGE INSTALLATION AND METHOD OFFORMING THE SAME John P. Craven, Akron, Ohio, assignor to The Babcock &Wilcox Company, Bockleigh, N. J., a corporation of New Janey ApplicationOctober 4, 1945, Serial No. 620,237

11 Claims. (01. 122-6) This invention relates to heat exchangeinstallations, and it is particularly adapted for advantageous use ininstallations in which high temperature furnace gases are utilized togenerate a gas or vapor in fluid carrying tubes connected into acirculation system. The invention involves a novel construction methodand a novel furnace wall as the product of that method.

The invention is particularly adapted for use in the erection of thewaterwall furnaces of water-tube steam generators in which upright watertubes serve as supports for the furnace wall. In the illustrative wall,steel sheets of large area are disposed tangentially across successivetubes and are welded thereto, gas or air leakage being substantiallyeliminated by seal welds joining adjacent sheets along their edges.

The combination, including a casing formed by such light weight metallicsheets welded to the exterior of the tubes and in thermal contacttherewith so that it attains the temperature of the contacted tubemetal, is particularly advantageous for high temperature fuel burningfurnaces and related heat exchange apparatus where the gases are undersuperatmcspheric pressure and where a draft tight wall is necessary. Theuse of comparatively thin sheets keeps the overall weight down andavoids the transmission of stresses to the tubes due to temperaturechanges in the casing.

Thermal insulation, to minimize the heat loss from the exterior, may beapplied as a plastic to the exterior surfaces of these sheets, and, toanchor this insulation, metallic studs are welded to the tubes throughthe sheets at distributed positions over the areas of the sheets andsealed with the sheets in unitary operations. These positions arepreferably directly opposite the 'tangency positions of the sheets andthe tubes, and the welding is so conducted that each weld also involvesthe inter-fusion of the tube metal and the sheet metal. Thus, each studis rigidly secured to a tube, and the interposed metallic sheet orcasing section is secured to both the tube and the stud by the sameoperation. Reticulated metal may be secured to the studs and spacedoutwardly of the casing sheets to anchor the thermal insulation when thelatter is installed as a plastic. In this case the reticulated metal maybe embedded in the insulation.

In the illustrative erection method, the studs may be quickly appliedover the areas of the casing sections by procedure involving the use ofa flash resistance welding device, the interposed easing sectionsprotecting the tube metal against overheating during the weldingprocess. This method also facilitates the use of a relatively thin sheetmetal to form a draft tight casing by eliminating the diflicult job ofaligning openings in the casing with studs previously applied directlyto the tubes.

The illustrative heat exchange installation, and the illustrative methodof construction, involve a marked reduction in fabrication costs due tothe single weld attachment of each stud through the imperforate metal ofthe sheets as compared to the previous practice of perforating thesheets and aligning the perforations with studs previously secured tothe wall tubes. Costs are further reduced by the utilization of flashresistance welding in welding the studs separately to the tubes throughthe casing sheets. The material and labor costs are much less than inother practices involving perforations of the sheets of the manual arcwelding and the sheets by forming plug type welds in the sheetperforations.

Another advantage of the illustrative installation and the illustrativemethod resides in the structural arrangement whereby the load of theexterior thermal insulation as transmitted to the studs is carrieddirectly to the tubes which form the structural support members for thewall, and only one weld intervenes between the load receiving portion ofthe stud and the tube.

The invention will be described by reference to the accompanyingdrawings, and other objects of the invention will appear as thedescription proceeds.

In the drawings:

Fig. l is a fragmentary view of the illustrative furnace wallconstruction, cut away at different positions for clarity of disclosure;

Fig. 2 is a view in the nature of a horizontal section, particularlyshowing the relationship of the casing, a stud, and a vapor generatingtube;

Fig. 3 is a diagrammatic view in the nature of a side elevationillustrating the manner of simultaneously weldin the studs and thecasing to the tubes; and

Fig. 4 is a horizontal section through the illustrative furnace wall.

The wall construction disclosed in the drawings is provided for use inthe erection of such steam generating installations as that shown in thepatent to Bailey, 2,357,300. The upright steam generating wall tubes actas supports for the wall, and the illustrative wall construction isapplicable to steam generating installations in which the furnace walltubes are spaced apart along the wall, as well as to those constructionsin which the wall tubes are substantially in contact, as illustrated inFigs. 1 and 3 of the present drawings. When the wall tubes are spacedapart, they may have metallic studs radially secured thereto, and ahighly refractory chrome ore composition may be installed as asemi-plastic around the studs and over the surfaces of the tubes. In theembodiment indicated in the drawings, such a highly refractory materialis installed as a plastic between the wall tubes Ill-ll, inclusive, andthe sheet metal casing section 20.

In the erection of the illustrative wall, the vapor generating tubes aresecured in their operative relationships to othe pressure parts of theinstallation, such as the upper and lower headers, steam and waterdrums, etc. Metallic casing sections are then disposed along the row oftubes in tangential relationship to their outer surface. Then studs aresecured by welding them to the tubes through the metal of the casingsections. This is accomplished by' forcing a stud member through thethin metallic sheet which is fused by the flow of electric currenttherethrough, the metal at the tube end of each stud and some of thetube metal being simultaneously fused. In this manner a good strengthweld is attained between the stud and the tube, and this weld also formsa seal weld between the periphcry of the stud projection and thesurroundin portion of the casing metal. The softening of the metal ofthe tube end of the stud, the adjacent sheet portion, and a part of thetube wall, and the pressure applied during the welding results in anupsetting so that the area of contact for strength and for heat transferbetween the sheet and the tube is appreciably greater than the originaldiameter of the stud.

This securement of the studs may be attained by using a stud weldingdevice of a type such as that shown by the patent to Anderson-2,360,-837, October 24, 1944, or by either of the types shown by the NelsonReissue Patent 22,314, May 11, 1943 or the Trainer at al.patent2,003,320, June 4, 1935. The illustrated welding device 22 hasthree adjustable feet such as those shown at 24 and 26 in the drawings.These feet are preferably equally circumferentially spaced and areadjusted so as to determine the correct position of a stud 30 when it isgripped in the chuck 32. The feet 24 and 26 are pressed against thecasing section 20 and the equipment i so adjusted and held that the studis directly over the position of tangency between the casing section 20and the tube H.

The welding operation effected by the resistance welding device 22 isthen initiated by pulling the trigger 34, it being understood that thetube and the stud in the chuck of the welding device are the electrodesof the welding electric circuit. In the operation of the device, thestud is withdrawn slightly from the casing section 20 to produce a metalfusing arc, and as soon as the effect of the arc has resulted inrelatively superficial fusion of the tube metal at the point of tube andcasing tangency, the stud 30 is fused and pressed into the fused metalof the casing section and the tube to form such a fusion zone as thatindicated at 38 in Fig. 2.

The entire operation of uniting a stud and easing section and a tubetakes but a few seconds so that a large number of the studs may beapplied over the areas of wide casing sections in a relatively shorttime.

After the studs such as 30 and 40-46, inclusive,

are applied in such an arrangement as that indicated in Fig. l, astratum 50 of thermal insulation is applied to the exterior surface ofthe casing section. This stratum is held in position by sheets ofreticulated metal such as that shown at 52. The studs project throughthe openings in the reticulated metal as indicated in Figs. 1 and 4, andthe metal is secured in its operative position by fasteners such as 54,55, and 56 which may be screw-threaded on to the studs.

Thereafter, joint screeds Ell-63, preferably of non-combustiblematerial, are secured to the reticulated metal 52 so as to designatewall areas or pockets in which the stratum 10 of thermal insulation maybe applied as a plastic. The screeds are also utilized in the insulationof this installation to obtain the desired thickness and surface of theinsulation material. Thereafter, other fastening devices such as 12 and14 (Fig. 4) are applied to hold the stratum ill in operativerelationship. These fastening devices, the ends of the studs, and theexterior surface of the installation stratum 10 may be then covered by ahard finish material 80 installed as a plastic. This material ispreferably one which will not only protect the exterior surface of thewall against mechanical damage, but which will also promote the thermalinsulation propertie of the wall.

By tightly fitting adjacent casing sections such as the section 20 overthe entire wall areas of the installation a draft-tight casing isprovided at a minimum expense, and the erection time for suchinstallations is materially reduced. The use of the invention eliminatessuch operations as the perforation of the casing sections to receivestuds which have previously been welded to the tubes, and in thisconnection, considerable erection time is saved because there is nonecessity for aligning the previously applied studs and perforations inthe casing sections, when the latter are applied.

By the interposition of the casing section 20 between a tube and a stud,the casing section acts as a shield to protect the tube againstexcessive fusion of tube metal, although, of course, the metal fusion islimited by the character of the electric arc and the time of itsapplication. These factors are determined in advance for studs, tubes,and casing sections of different materials and different thicknesses.

When the metallic sheets for the casing sections are of carbon steel andthe tubes and headers associated therewith are of the same material, theheat transfer between the casing sheets and the outer tube wall will besuch that these components operate at substantially the sametemperatures, thus eliminating the setting up of damaging temperaturestresses between them. Conditions such as furnace temperatures or gastemperatures affecting the interior surface of the wall, or the spacingof the wall tubes may be such as to cause the average temperature of thecasing sheets to differ materially from that of the pressure parts, andin such cases the invention contemplates the use of sheets of such ametal or alloy that they will have a coefficient of expansion which isgreater than that of the pressure parts. Chrome nickel alloys oraluminum and some of its alloys have such coeiiicients of expansion.When the casing sheets are disposed at a greater distance from the planeof the tube axes, and particularly when the tubes are spaced apart sothat more heat is transmitted between the intertube spaces, a change inthe average temperature of the casing is efiected. In this instance,although the stud would pierce the metal of the tube sheet and be weldedto the tube for a strength weld, the sheet would not be tangent to thetubes.

It is to be understood that the terms such as sheet metal, thin metallicsheets, and flat metal casing sections or similar terms, used herein areintended to cover metal members sometimes referred to in the art assheets, and

sometimes referred to as plates.

I claim:

1. In a tubular heat exchanger, a row of spaced wall tubes normallysubject externally to a heat exchange medium, and closure means for thespaces between the tubes disposed externally of the plane of the tubeaxes, said closure means including imperforate thin metallic sheetsextending transversely over a plurality of tubes and longitudinallythereof in spaced relationship with the plane of the tube axes, metallicstuds extending substantially outwardly from the rear faces of the tubeswhich are covered by the sheets, said studs being secured in pressuretight union with the sheets and the tubes by unitary welds.

2. In a fluid heating installation, fluid heating tubes having theirouter surfaces exposed to high temperature gases, a draft-tight metalliccasing including sections of sheet metal extending tangentially acrosssuccessive tubes, insulation anchoring studs welded to said sections andextending outwardly therefrom at positions substantially registeringwith the points of tube and section tangency, each stud being secured bya single weld which unites a tube and a casing section as well as thestud and the tube, and thermal insulation covering the exterior sides ofthe sec= tions and anchored thereon by the studs.

'3. In the erection of a tubular heat exchanger, erecting a row of walltubes connected into their operative relationship with other circulatoryparts of the exchanger, applying sheet metal casing sections acrosssuccessive tubes and tangentially thereof, and welding the sections tothe tubes by welding insulation anchoring studs to exterior surfaces ofthe sections at positions registering with the points of tangency of thesections to the tubes, the unitary weld at the inner end of each studextending axially of the stud and including some of the tube metal.

4. In the art of constructing steam generator installations, disposingsteam generating wall tubes in operative relationship to other pressureparts, juxtaposing imperforate metallic casing sections across and intangential relationship to successive tubes, securing said casingsections to the tubes by welding insulation attachment anchors to theexterior faces of the sections at positions in radial alignment with thepositions of tangency contact between the tubes and said sections, andthen applying thermal insulation about said anchors and over theexterior faces of said sections.

5. In the erection of tubular heat exchangers, erecting a row of walltubes, positioning sheet metal casing sections tangentially across theerected tubes, and welding the sections to the tubes by weldinginsulation anchoring studs to exterior surfaces of the sections atpositions substantially registering with the points of tangency of thesections to the tubes.

6. In a fluid heating installation, fluid heating tubes normally exposedto high temperature gases, draft tight sheet metal casing sections 8extending tangentially across a plurality of successive tubes,insulation anchoring studs secured to said sections and extendingoutwardly therefrom at positions substantially registering with thepositions of tube and section tangency. a unitary weld at the inner endof each stud extending axially of the stud and including some of themetal of a casing section and a tube, and a thermal insulation stratumcovering the exterior sides of the sections and anchored thereon by thestuds, the studs extending outwardly through said stratum.

'7. In the art of steam generation, erecting steam generating tubes intheir operative relationships with other components of a steamgenerator, disposing sheet metal casing sections across the tubes withtheir interior surfaces in tangential relation to the tubes, and weldinginsulation anchoring studs endwise to the exterior surfaces of thecasing sections at positions in radial alignment with the positions oftube and easing section contact, the fusion of said welding alsoextending through the sections and into the tube metal at saidpositions.

8. In the erection of tubular heat exchangers, erecting a row of walltubes in operative relationsloip to other circulatory parts of theexchanger, iuxtaposing sheet metal casing sections tangentially acrosssaid tubes and exteriorly thereof, and welding said sections to theerected tubes by end welding insulation anchoring studs to the exteriorsurfaces of the sections at positions substantially registering with thepoints of tangency of the sections to the tubes.

9. In a fluid heat exchange installation, fluid heating tubes disposedin row arrangement and having their outer surfaces exposed to hightemperature gases, draft-tight sheet metal casing sections disposedtangentially across successive tubes, insulation anchoring studs securedto said sections and extending outwardly therefrom at pointssubstantially registering with the positions of tube and sectiontangency, a single unitary weld at the inner end of each stud extend ingaxially of the stud and including metal of a casing section and a tube,and thermal insulation covering the exterior sides of the sections andanchored thereon by the studs.

10. In a method of fabricating the wall of a fluid heat exchange devicehaving wall tubes secured to a wall including a section of flat metaldisposed exteriorly of the tubes, the method comprising juxtaposing thesection and a tube in operative relationship, and securing the wall tothe tube by welding through imperforate portions of the wall wholly frompositions exteriorly of the wall and on the side of the wall sectionopposite that side contacted by the tubes and with the addition of metalfrom similar positions for the separate welds.

11. In a method of fabricating the wall of a fluid heat exchange devicehaving waii secured to a wall including a section of flat metal disposedexteriorly of the tubes, the method comprising juxtaposing the wall anda tube in operative relationship, securing the wall to the tube bywelding studs through imperforate por tions of the wall wholly frompositions exteriorly of the wall and on the side of the wall sectionopposite that side contacted by the tubes, and disposing thermalinsulation exteriorly of the wall by the use of the studs as securingdevices.

JOHN P. CRAVEN.

(References on following page:

The following references are of record in the 7 REFERENCES crmn file ofthis patent:

UNITED STATES PATENTS Nfimber Re. 22,108 1,761,567

Number 8 Name Date Murray Aug. 26, 1930 Bailey Dec. 4, 1934 Andrus Oct.29, 1940 Bailey Apr. 22, 1941 Benson Dec. 29, 1942 Anderson Oct. 24,1944

